INVESTMENTS IN OPERATING PARTNERSHIPS (Details 3) (USD $)	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Revenues
Rental	$ 29,398,505		$ 33,139,905
Interest and other	789,309		946,955
Operating Partnerships Revenues	30,187,814		34,086,860
Expenses
Interest	5,205,191		6,389,626
Depreciation and amortization	8,352,808		9,851,546
Operating expenses	20,387,995		21,953,822
Operating Partnerships Total Expenses	33,945,994		38,194,994
NET LOSS	(3,758,180)		(4,108,134)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(3,720,595)	[1]	(4,067,049)	[1]
Net loss allocated to other Partners	(37,585)		(41,085)
Series Twenty [Member]
Revenues
Rental	455,802		661,277
Interest and other	18,313		9,074
Operating Partnerships Revenues	474,115		670,351
Expenses
Interest	90,941		124,387
Depreciation and amortization	131,612		162,247
Operating expenses	382,175		459,324
Operating Partnerships Total Expenses	604,728		745,958
NET LOSS	(130,613)		(75,607)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(129,307)	[2]	(74,851)	[2]
Net loss allocated to other Partners	(1,306)		(756)
Series Twenty One [Member]
Revenues
Rental	472,382		490,086
Interest and other	5,775		6,035
Operating Partnerships Revenues	478,157		496,121
Expenses
Interest	122,484		125,449
Depreciation and amortization	78,762		90,309
Operating expenses	294,041		296,220
Operating Partnerships Total Expenses	495,287		511,978
NET LOSS	(17,130)		(15,857)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(16,959)	[3]	(15,698)	[3]
Net loss allocated to other Partners	(171)		(159)
Series Twenty Two [Member]
Revenues
Rental	377,666		432,208
Interest and other	11,454		6,463
Operating Partnerships Revenues	389,120		438,671
Expenses
Interest	69,012		74,144
Depreciation and amortization	87,225		101,660
Operating expenses	285,714		324,028
Operating Partnerships Total Expenses	441,951		499,832
NET LOSS	(52,831)		(61,161)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(52,303)	[4]	(60,549)	[4]
Net loss allocated to other Partners	(528)		(612)
Series Twenty Three [Member]
Revenues
Rental	768,587		777,025
Interest and other	31,082		33,334
Operating Partnerships Revenues	799,669		810,359
Expenses
Interest	123,125		133,817
Depreciation and amortization	178,819		170,071
Operating expenses	584,298		516,424
Operating Partnerships Total Expenses	886,242		820,312
NET LOSS	(86,573)		(9,953)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(85,706)	[5]	(9,852)	[5]
Net loss allocated to other Partners	(867)		(101)
Series Twenty Four [Member]
Revenues
Rental	286,615		547,649
Interest and other	4,437		11,597
Operating Partnerships Revenues	291,052		559,246
Expenses
Interest	34,720		78,191
Depreciation and amortization	80,376		167,495
Operating expenses	219,241		373,268
Operating Partnerships Total Expenses	334,337		618,954
NET LOSS	(43,285)		(59,708)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(42,852)	[6]	(59,111)	[6]
Net loss allocated to other Partners	(433)		(597)
Series Twenty Five [Member]
Revenues
Rental	237,018		330,118
Interest and other	4,451		5,673
Operating Partnerships Revenues	241,469		335,791
Expenses
Interest	38,469		53,419
Depreciation and amortization	67,323		81,318
Operating expenses	156,776		273,747
Operating Partnerships Total Expenses	262,568		408,484
NET LOSS	(21,099)		(72,693)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(20,888)	[7]	(71,966)	[7]
Net loss allocated to other Partners	(211)		(727)
Series Twenty Six [Member]
Revenues
Rental	905,408		1,430,194
Interest and other	18,706		76,918
Operating Partnerships Revenues	924,114		1,507,112
Expenses
Interest	122,241		259,143
Depreciation and amortization	275,742		469,647
Operating expenses	737,004		1,067,822
Operating Partnerships Total Expenses	1,134,987		1,796,612
NET LOSS	(210,873)		(289,500)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(208,764)	[8]	(286,605)	[8]
Net loss allocated to other Partners	(2,109)		(2,895)
Series Twenty Seven [Member]
Revenues
Rental	1,126,919		1,377,433
Interest and other	28,732		16,709
Operating Partnerships Revenues	1,155,651		1,394,142
Expenses
Interest	235,822		286,600
Depreciation and amortization	252,049		315,420
Operating expenses	755,332		813,078
Operating Partnerships Total Expenses	1,243,203		1,415,098
NET LOSS	(87,552)		(20,956)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(86,676)	[9]	(20,746)	[9]
Net loss allocated to other Partners	(876)		(210)
Series Twenty Eight [Member]
Revenues
Rental	1,156,404		1,711,027
Interest and other	21,660		23,901
Operating Partnerships Revenues	1,178,064		1,734,928
Expenses
Interest	131,567		293,430
Depreciation and amortization	377,166		476,903
Operating expenses	802,155		1,160,120
Operating Partnerships Total Expenses	1,310,888		1,930,453
NET LOSS	(132,824)		(195,525)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(131,496)	[10]	(193,570)	[10]
Net loss allocated to other Partners	(1,328)		(1,955)
Series Twenty Nine [Member]
Revenues
Rental	1,511,882		1,955,470
Interest and other	43,975		48,632
Operating Partnerships Revenues	1,555,857		2,004,102
Expenses
Interest	255,825		349,173
Depreciation and amortization	530,949		651,061
Operating expenses	1,001,753		1,326,824
Operating Partnerships Total Expenses	1,788,527		2,327,058
NET LOSS	(232,670)		(322,956)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(230,343)	[11]	(319,726)	[11]
Net loss allocated to other Partners	(2,327)		(3,230)
Series Thirty [Member]
Revenues
Rental	1,170,681		1,143,464
Interest and other	16,822		33,537
Operating Partnerships Revenues	1,187,503		1,177,001
Expenses
Interest	147,232		152,492
Depreciation and amortization	260,902		249,766
Operating expenses	973,235		896,097
Operating Partnerships Total Expenses	1,381,369		1,298,355
NET LOSS	(193,866)		(121,354)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(191,927)	[12]	(120,140)	[12]
Net loss allocated to other Partners	(1,939)		(1,214)
Series Thirty One [Member]
Revenues
Rental	2,399,552		2,453,810
Interest and other	85,519		72,987
Operating Partnerships Revenues	2,485,071		2,526,797
Expenses
Interest	333,358		380,237
Depreciation and amortization	670,334		716,682
Operating expenses	1,713,648		1,672,169
Operating Partnerships Total Expenses	2,717,340		2,769,088
NET LOSS	(232,269)		(242,291)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(229,946)	[13]	(239,868)	[13]
Net loss allocated to other Partners	(2,323)		(2,423)
Series Thirty Two [Member]
Revenues
Rental	1,358,815		1,458,766
Interest and other	54,886		54,936
Operating Partnerships Revenues	1,413,701		1,513,702
Expenses
Interest	254,963		294,133
Depreciation and amortization	513,367		544,169
Operating expenses	947,043		994,795
Operating Partnerships Total Expenses	1,715,373		1,833,097
NET LOSS	(301,672)		(319,395)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(298,655)	[14]	(316,201)	[14]
Net loss allocated to other Partners	(3,017)		(3,194)
Series Thirty Three [Member]
Revenues
Rental	688,602		661,949
Interest and other	19,467		22,297
Operating Partnerships Revenues	708,069		684,246
Expenses
Interest	141,616		144,239
Depreciation and amortization	229,209		229,802
Operating expenses	465,812		434,486
Operating Partnerships Total Expenses	836,637		808,527
NET LOSS	(128,568)		(124,281)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(127,282)	[15]	(123,038)	[15]
Net loss allocated to other Partners	(1,286)		(1,243)
Series Thirty Four [Member]
Revenues
Rental	1,366,358		1,445,327
Interest and other	34,560		41,334
Operating Partnerships Revenues	1,400,918		1,486,661
Expenses
Interest	191,109		216,240
Depreciation and amortization	469,635		476,764
Operating expenses	981,469		930,394
Operating Partnerships Total Expenses	1,642,213		1,623,398
NET LOSS	(241,295)		(136,737)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(238,882)	[16]	(135,370)	[16]
Net loss allocated to other Partners	(2,413)		(1,367)
Series Thirty Five [Member]
Revenues
Rental	1,127,641		1,091,046
Interest and other	41,752		40,215
Operating Partnerships Revenues	1,169,393		1,131,261
Expenses
Interest	195,502		203,764
Depreciation and amortization	349,834		370,326
Operating expenses	706,211		710,534
Operating Partnerships Total Expenses	1,251,547		1,284,624
NET LOSS	(82,154)		(153,363)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(81,332)	[17]	(151,829)	[17]
Net loss allocated to other Partners	(822)		(1,534)
Series Thirty Six [Member]
Revenues
Rental	742,396		739,281
Interest and other	15,338		18,769
Operating Partnerships Revenues	757,734		758,050
Expenses
Interest	139,311		140,851
Depreciation and amortization	209,029		226,886
Operating expenses	489,490		534,342
Operating Partnerships Total Expenses	837,830		902,079
NET LOSS	(80,096)		(144,029)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(79,295)	[18]	(142,589)	[18]
Net loss allocated to other Partners	(801)		(1,440)
Series Thirty Seven [Member]
Revenues
Rental	1,137,309		1,124,113
Interest and other	26,421		29,831
Operating Partnerships Revenues	1,163,730		1,153,944
Expenses
Interest	174,250		160,669
Depreciation and amortization	337,691		394,435
Operating expenses	946,451		862,315
Operating Partnerships Total Expenses	1,458,392		1,417,419
NET LOSS	(294,662)		(263,475)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(291,715)	[19]	(260,840)	[19]
Net loss allocated to other Partners	(2,947)		(2,635)
Series Thirty Eight [Member]
Revenues
Rental	951,294		904,723
Interest and other	20,770		16,637
Operating Partnerships Revenues	972,064		921,360
Expenses
Interest	184,014		181,654
Depreciation and amortization	243,943		242,647
Operating expenses	592,524		592,883
Operating Partnerships Total Expenses	1,020,481		1,017,184
NET LOSS	(48,417)		(95,824)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(47,933)	[20]	(94,866)	[20]
Net loss allocated to other Partners	(484)		(958)
Series Thirty Nine [Member]
Revenues
Rental	697,952		687,199
Interest and other	21,580		21,580
Operating Partnerships Revenues	719,532		708,779
Expenses
Interest	131,620		128,590
Depreciation and amortization	197,777		225,230
Operating expenses	544,512		491,348
Operating Partnerships Total Expenses	873,909		845,168
NET LOSS	(154,377)		(136,389)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(152,833)	[21]	(135,025)	[21]
Net loss allocated to other Partners	(1,544)		(1,364)
Series Forty [Member]
Revenues
Rental	1,023,102		1,023,872
Interest and other	26,197		26,354
Operating Partnerships Revenues	1,049,299		1,050,226
Expenses
Interest	204,466		242,209
Depreciation and amortization	268,786		329,794
Operating expenses	732,846		785,718
Operating Partnerships Total Expenses	1,206,098		1,357,721
NET LOSS	(156,799)		(307,495)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(155,231)	[22]	(304,420)	[22]
Net loss allocated to other Partners	(1,568)		(3,075)
Series Forty One [Member]
Revenues
Rental	1,403,193		1,388,428
Interest and other	35,027		35,370
Operating Partnerships Revenues	1,438,220		1,423,798
Expenses
Interest	283,929		290,163
Depreciation and amortization	360,227		563,850
Operating expenses	898,162		764,691
Operating Partnerships Total Expenses	1,542,318		1,618,704
NET LOSS	(104,098)		(194,906)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(103,057)	[23]	(192,957)	[23]
Net loss allocated to other Partners	(1,041)		(1,949)
Series Forty Two [Member]
Revenues
Rental	1,566,628		1,601,125
Interest and other	61,605		45,726
Operating Partnerships Revenues	1,628,233		1,646,851
Expenses
Interest	297,270		323,803
Depreciation and amortization	415,854		439,472
Operating expenses	973,628		936,930
Operating Partnerships Total Expenses	1,686,752		1,700,205
NET LOSS	(58,519)		(53,354)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(57,934)	[24]	(52,820)	[24]
Net loss allocated to other Partners	(585)		(534)
Series Forty Three [Member]
Revenues
Rental	1,924,225		1,870,431
Interest and other	61,516		60,738
Operating Partnerships Revenues	1,985,741		1,931,169
Expenses
Interest	313,111		354,931
Depreciation and amortization	545,949		542,379
Operating expenses	1,270,964		1,138,874
Operating Partnerships Total Expenses	2,130,024		2,036,184
NET LOSS	(144,283)		(105,015)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(142,840)	[25]	(103,965)	[25]
Net loss allocated to other Partners	(1,443)		(1,050)
Series Forty Four [Member]
Revenues
Rental	1,451,376		1,987,330
Interest and other	31,859		73,412
Operating Partnerships Revenues	1,483,235		2,060,742
Expenses
Interest	407,160		591,617
Depreciation and amortization	380,591		594,764
Operating expenses	806,806		1,073,797
Operating Partnerships Total Expenses	1,594,557		2,260,178
NET LOSS	(111,322)		(199,436)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(110,209)	[26]	(197,442)	[26]
Net loss allocated to other Partners	(1,113)		(1,994)
Series Forty Five [Member]
Revenues
Rental	1,707,070		2,475,615
Interest and other	30,055		70,198
Operating Partnerships Revenues	1,737,125		2,545,813
Expenses
Interest	277,250		496,552
Depreciation and amortization	493,165		710,450
Operating expenses	1,227,896		1,606,885
Operating Partnerships Total Expenses	1,998,311		2,813,887
NET LOSS	(261,186)		(268,074)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(258,574)	[27]	(265,393)	[27]
Net loss allocated to other Partners	(2,612)		(2,681)
Series Forty Six [Member]
Revenues
Rental	1,383,628		1,370,939
Interest and other	17,350		44,698
Operating Partnerships Revenues	1,400,978		1,415,637
Expenses
Interest	304,824		309,729
Depreciation and amortization	346,492		307,999
Operating expenses	898,809		916,709
Operating Partnerships Total Expenses	1,550,125		1,534,437
NET LOSS	(149,147)		(118,800)
Net loss allocated to Boston Capital Tax Credit Fund IV L.P.	(147,656)	[28]	(117,612)	[28]
Net loss allocated to other Partners	$ (1,491)		$ (1,188)

[1] Amounts include $(3,473,893) and $(3,574,669) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[2] Amounts include $(129,307) and $(74,851) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[3] Amounts include $(16,959) and $(15,698) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[4] Amounts include $(52,303) and $(60,549) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[5] Amounts include $(85,706) and $(9,852) for 2014 and 2013, of net loss not recognized under the equity method of accounting.

[6] Amounts include $(42,852) and $(59,111) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[7] Amounts include $(20,888) and $(71,966) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[8] Amounts include $(208,764) and $(286,605) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[9] Amounts include $(86,676) and $(20,746) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[10] Amounts include $(131,496) and $(193,570) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[11] Amounts include $(230,343) and $(319,726) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[12] Amounts include $(191,927) and $(120,140) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[13] Amounts include $(229,946) and $(239,868) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[14] Amounts include $(298,655) and $(316,201) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[15] Amounts include $(127,282) and $(123,038) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[16] Amounts include $(238,882) and $(135,370) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[17] Amounts include $(81,332) and $(151,829) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[18] Amounts include $(79,295) and $(142,589) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[19] Amounts include $(291,715) and $(260,840) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[20] Amounts include $(47,933) and $(94,866) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[21] Amounts include $(152,833) and $(135,025) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[22] Amounts include $(155,231) and $(304,420) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[23] Amounts include $(103,057) and $(192,957) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[24] Amounts include $(57,934) and $(9,900) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[25] Amounts include $(137,415) and $(7,958) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[26] Amounts include $(110,209) and $(168,794) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[27] Amounts include $(136,011) and $(58,200) for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.

[28] Amounts include $(28,942) and $- for 2014 and 2013, respectively, of net loss not recognized under the equity method of accounting.